Until now the mechanisms of how recent historical land-use (hereafter called "habitat") changes in island ecosystems shape the distribution of individual insect species have been poorly understood in the field of conservation biology. In the present study we concentrate on the delicate equilibrium of the contribution of habitat island composition (i.e. habitat resource availability) with respect to island insect distribution patterns. In this context we study in detail the distribution patterns of four functional groups (herbivorous sucking insects, herbivorous chewing insects, spiders and other arthropod predators) of endemic, native and exotic arthropod species in a well-studied island of the Azores archipelago (Terceira). Within the bigger context of a standardized sampling program both for epigean and canopy insects and spiders we want to find out which species are truly rare and which are pseudo-rare species in each target habitat. Two dimensions of rarity were measured: abundance and habitat specialization. Two domains of rarity were identified: "among habitats" and "geographic". Some interesting patterns emerged. The high dispersal abilities of many insect and spider species together with the fact that many species from islands tend to be generalists imply that many species tend to be vagrants in several habitats and consequently are locally habitat pseudo-rarities. Two types of local pseudorare species were identified: "habitat (or land-use)" and "host plant" pseudorarities. Some species are rare in one habitat type whilst they are more common in another...

Spatial patterns in biodiversity variation at a regional scale are rarely taken into account when a natural reserve is to be established, despite many available methods for determining them. In this paper, we used dimensions of occurrence of 105 species of Anura (Amphibia) in the cerrado region of central Brazil to create a regional system of potential areas that preserves all regional diversity, using three different algorithms to establish reserve networks: "greedy", rarity, and simulated annealing algorithms. These generated networks based on complementarity with 10, 12, and 8 regions, respectively, widely distributed in the biome, and encompassing various Brazilian states. Although the purpose of these algorithms is to find a small number of regions for which all species are represented at least once, the results showed that 67.6%, 76.2%, and 69.5% of the species were represented in two or more regions in the three networks. Simulated annealing produced the smallest network, but it left out three species (one endemic). On the other hand, while the greedy algorithm produce a smaller solution, the rarity-based algorithm ensured that more species were represented more than once, which can be advantageous because it takes into consideration the high levels of habitat loss in the cerrado. Although usually coarse...

Standard economic theory predicts that exploitation alone is unlikely to result in species extinction because of the escalating costs of finding the last individuals of a declining species. We argue that the human predisposition to place exaggerated value on rarity fuels disproportionate exploitation of rare species, rendering them even rarer and thus more desirable, ultimately leading them into an extinction vortex. Here we present a simple mathematical model and various empirical examples to show how the value attributed to rarity in some human activities could precipitate the extinction of rare species—a concept that we term the anthropogenic Allee effect. The alarming finding that human perception of rarity can precipitate species extinction has serious implications for the conservation of species that are rare or that may become so, be they charismatic and emblematic or simply likely to become fashionable for certain activities.

We explore variation in the prices paid by recreational hunters of trophy animals in Africa and its possible causes, including perceived rarity. Previous work has raised the possibility that extinction can result if demand rises fast enough as a species becomes rarer. We attempt to disentangle this from other inter-correlated influences affecting price. Species with larger body sizes and larger trophies were more valuable. Value increased less steeply as a function of size for bovids than for felids and the effect was consistent across countries. Power laws, ubiquitous in physical and social systems, described the trends. The exponent was approximately 0.4 for bovids, compared with approximately 1.0 for felids. Rarity (as indexed by IUCN score) influenced the value of bovid trophies – price was higher for species in categories denoting higher global threat. There was substantial variation in price among and within families not explained by either size or rarity. This may be attributable to a ‘charisma’ effect, which seems likely to be a general attribute of human perceptions of wildlife. Species where prices were higher than predicted by size or rarity are ranked high in published accounts of desirability by hunters. We conclude that the valuation of these species is explicable to a large extent by body size and perceived rarity...

We investigated the conservation concern of Azorean forest fragments and the entire Terceira Island surface using arthropod species vulnerability as defined by the Kattan index, which is based on species rarity. Species rarity was evaluated according to geographical distribution (endemic vs. non endemic species), habitat specialization (distribution across biotopes) and population size (individuals collected in standardized samples). Geographical rarity was considered at ‘global’ scale (species endemic to the Azorean islands) and ‘regional’ scale (single island endemics).

Among various potential consequences of rarity is genetic erosion. Neutral genetic theory predicts that rare species will have lower genetic diversity than common species. To examine the association between genetic diversity and rarity, variation at eight DNA microsatellite markers was documented for 14 Acropora species that display different patterns of distribution and abundance in the Indo–Pacific Ocean. Our results show that the relationship between rarity and genetic diversity is not a positive linear association because, contrary to expectations, some rare species are genetically diverse and some populations of common species are genetically depleted. Our data suggest that inbreeding is the most likely mechanism of genetic depletion in both rare and common corals, and that hybridization is the most likely explanation for higher than expected levels of genetic diversity in rare species. A significant hypothesis generated from our study with direct conservation implications is that as a group, Acropora corals have lower genetic diversity at neutral microsatellite loci than may be expected from their taxonomic diversity, and this may suggest a heightened susceptibility to environmental change. This hypothesis requires validation based on genetic diversity estimates derived from a large portion of the genome.

Rarity is widely used to predict the vulnerability of species to extinction. Species can be rare in markedly different ways, but the relative impacts of these different forms of rarity on extinction risk are poorly known and cannot be determined through observations of species that are not yet extinct. The fossil record provides a valuable archive with which we can directly determine which aspects of rarity lead to the greatest risk. Previous palaeontological analyses confirm that rarity is associated with extinction risk, but the relative contributions of different types of rarity to extinction risk remain unknown because their impacts have never been examined simultaneously. Here, we analyse a global database of fossil marine animals spanning the past 500 million years, examining differential extinction with respect to multiple rarity types within each geological stage. We observe systematic differences in extinction risk over time among marine genera classified according to their rarity. Geographic range played a primary role in determining extinction, and habitat breadth a secondary role, whereas local abundance had little effect. These results suggest that current reductions in geographic range size will lead to pronounced increases in long-term extinction risk even if local populations are relatively large at present.

In decisions on nature conservation measures, we depend largely on knowledge of the relationship between threats and environmental factors for a very limited number of species groups, with relevant environmental factors often being deduced from the relationship between threat and species traits. But can relationships between traits and levels of threats be identified across species from completely different taxonomic groups; and how accurately do well-known taxonomic groups indicate levels of threat in other species groups? To answer these questions, we first made a list of 152 species attributes of morphological and demographic traits and habitat requirements. Based on these attributes we then grew random forests of decision trees for 1183 species in the 18 different taxonomic groups for which we had Red Lists available in the Netherlands, using these to classify animals, plants, and mushrooms according to their rarity and decline. Finally, we grew random forests for four species groups often used as indicator groups to study how well the relationship between attribute and decline within these groups reflected that relationship within the larger taxonomic group to which these groups belong. Correct classification of rarity based on all attributes was as high as 88% in animals...

The copyright to this article passed from the Ecological Society of America to the Resilience Alliance on 1 January 2000.
Published in the Journal Ecology and Society (formerly Conservation Ecology); We examined patterns of commonness and rarity among plant species in montane wet grasslands of Iberia. This examination is set within two contexts. First, we expanded on an earlier scheme for classifying species as common or rare by adding a fourth criterion, the ability of that species to occupy a larger or smaller fraction of its potential suitable habitats, i.e., habitat occupancy. Second, we explicated two theories, the superior organism theory and the generalist/specialist trade-off theory. The data consisted of 232 species distributed among 92 plots. The species were measured for mean local abundance, size of environmental volume occupied, percentage of volume occupied, range within Iberia, and range in Europe and the Mediterranean basin. In general, all measures were positively correlated, in agreement with the superior organism theory. However, specialist species were also found. Thus, patterns of commonness and rarity may be due to a combination of mechanisms. Analyses such as ours can also be used as a first step in identifying habitats and species that may be endangered.; Funding was provided by the projects "Humedales en áreas de descarga de acuíferos en territorios graníticos (Sierra de Guadarrama)" (Comunidad Autónoma de Madrid nº C129/91)...

While it is a truism that species rarity is non-randomly distributed across regions, habitats, and taxa, there is little consensus on which factors are the best predictors of low abundances and restricted geographical ranges. In this study, we evaluate the effects of ecological and life-history traits, as well as phylogeny, on rarity in the abundance and distribution of land birds inhabiting forest habitats in the Mediterranean and temperate regions of Chile. We use data on abundance collected at 16 sites and data on latitudinal distribution obtained from a literature compilation. Statistical analyses were based on multiple regression and multivariate models. We used Signed Mantel test to analyse the relationship between species ecological and life-history traits and rarity, taking into account the effect of phylogenetic relatedness. We found that rarity, in terms of distribution, is associated with a low investment in reproduction, non-migratory status, and degree of habitat specialization. These ecological and life-history traits, in association with forest loss due to climatic changes and human impacts, may explain the narrow distribution of most endemic forest birds species. Rarity in abundance, on the other hand, is more difficult to explain. However...

Image enhancement is an important image processing technique that processes
images suitably for a specific application e.g. image editing. The conventional
solutions of image enhancement are grouped into two categories which are
spatial domain processing method and transform domain processing method such as
contrast manipulation, histogram equalization, homomorphic filtering. This
letter proposes a new image enhance method based on dictionary learning.
Particularly, the proposed method adjusts the image by manipulating the rarity
of dictionary atoms. Firstly, learn the dictionary through sparse coding
algorithms on divided sub-image blocks. Secondly, compute the rarity of
dictionary atoms on statistics of the corresponding sparse coefficients.
Thirdly, adjust the rarity according to specific application and form a new
dictionary. Finally, reconstruct the image using the updated dictionary and
sparse coefficients. Compared with the traditional techniques, the proposed
method enhances image based on the image content not on distribution of pixel
grey value or frequency. The advantages of the proposed method lie in that it
is in better correspondence with the response of the human visual system and
more suitable for salient objects extraction. The experimental results
demonstrate the effectiveness of the proposed image enhance method.; Comment: 2 pages...

This paper investigates the influence of environmental noise on the
characteristic timescale of the dynamics of density-dependent populations.
General results are obtained on the statistics of time spent in rarity and time
spent in commonness. The nonlinear stochastic models under consideration form a
class of Markov chains on the state space $]0, \infty[$ which are transient if
the intrinsic growth rate is negative and recurrent if it is positive or null.
In the recurrent case, we obtain a necessary and sufficient condition for
positive recurrence and precise estimates for the distribution of times of
rarity and commonness. In the null recurrent, critical case that applies to
ecologically neutral species, the distribution of rarity time is a universal
power law with exponent -3/2. These non- trivial results should be of interest
to biologists involved in the conservation of threatened populations, and to
epidemiologists facing the need to better understanding the dynamics of pest or
disease outbreaks.

Comparative studies investigating relationships between plant traits and species rarity and commonness were surveyed to establish whether global patterns have emerged that would be of practical use in management strategies aimed at the long-term conservation of species. Across 54 studies, 94 traits have been examined in relation to abundance, distribution and threatened status at local, regional and geographical spatial scales. Most traits (63) have yet to be the focus of more than one study. Half of the studies involved less than 10 species, and one-quarter did not replicate rare-common contrasts. Although these features of the literature make it difficult to demonstrate robust generalizations regarding trait relationships with species rarity, some important findings surfaced in relation to traits that have been examined in two or more studies. Species with narrow geographical distributions were found to produce significantly fewer seeds (per unit measurement) than common species (in four of six studies), but did not differ with respect to breeding system (five of five studies). The majority of traits (including seed size, competitive ability, growth form and dispersal mode) were related to rarity in different ways from one study to the next. The highly context-dependent nature of most trait relationships with rarity implies that application of knowledge concerning rare-common differences and similarities to management plans will vary substantially for different vegetation types and on different continents. A comparative analysis of distribution patterns in relation to several life-history and ecological traits among 700 Australian eucalypt species was then performed. A significantly disproportionate number of tall species and species with long flowering durations had wide geographical ranges. Trait relationships with distribution were explored further through the development of a methodology incorporating multiple spatial scales. Eight theoretical categories were described illustrating variation in distribution patterns (and hence rarity and commonness) across small...

Aim The causes of orchid diversification and intrinsic rarity are poorly resolved. The Orchidaceae of the Southwest Australian Floristic Region use a diversity of pollination strategies and sites of mycorrhizal infection, and occupy a diversity of habitats. We combined a biogeographic analysis with analysis of factors associated with rarity to establish: (1) the landscape features correlated with taxon turnover and speciation, and (2) the possible role in taxon rarity of geographic region, pollination strategy, edaphic habitat and site of mycorrhizal infection. Location Southwest Australian Floristic Region. Methods The distributions of 407 orchid taxa (species and subspecies) were mapped at the quarter-degree scale using 13,267 collections in the Western Australian Herbarium. This database was used to map taxon richness, for a biogeographic analysis and to quantify rarity of taxa. Using herbarium records, rarity was expressed as mean abundance, mean distribution and incidence of rarity based on abundance and distribution for each genus. We tested for differences in rarity of species between pollination strategies, edaphic habitats and sites of mycorrhizal infection. Results Taxon richness was highest in the High Rainfall Province. Biogeographic provincial boundaries for orchids were aligned with rainfall...

Across the globe, biodiversity loss is occurring at an unprecedented rate. Rare species are especially susceptible to extinction, given that they typically have small population sizes and restricted geographic ranges, are less adaptable to disturbances, and are greater habitat specialists. However, while rare species may be prone to extinction, it remains unclear whether the loss of rare species is important to ecosystem function. In addition, it is important to consider the way in which rarity is defined, given that there are multiple definitions of rarity based on a species' geographic range, habitat specificity, and abundance in a community. Therefore, to better understand the contribution of rare species to community function, our study has two goals: 1) to determine whether rare species contribute to community trait space, which serves as a proxy for ecosystem function, more than common species; 2) to determine if the effect of rare species differs based on the definition of rarity employed. Using grassland data from Cedar Creek Minnesota, we assessed the importance of rare species on community trait space. We found that rare species have an equal effect on trait space as common species, except in the case of rarity defined as mean abundance. This suggests that when defining rarity by geographic range and habitat specificity...

This research will present some definitions of what is a rare work from theories of authors and bibliophiles who discuss the theme, demonstrating the view that each one highlights on the bibliographical rarity, and the synthesis of the relation of the concept of rare work presented by these authors, we present a analysis methodology for bibliographical rarity also addressing the importance of having a study of the technical treatment of the rare books of UFMT Central Library and ending with the relevance and benefits of having a manual defining the criteria for bibliographical rarity in an institution.; A presente pesquisa apresentará algumas definições do que é uma obra rara partindo de teorias de autores e bibliófilos que discutem o tema, demonstrando o ponto de vista que cada um ressalta referente à raridade bibliográfica, e a síntese da relação do conceito de obra rara apresentada por esses autores, será apresentada uma metodologia de análise para raridade bibliográfica tratando também da importância de se ter um estudo do tratamento técnico das obras raras da Biblioteca Central da UFMT e finalizando com a relevância e os benefícios de se ter um manual definindo os critérios para raridade bibliográfica em uma instituição.